BOSTON — A three-alarm fire in Boston's Dorchester neighborhood that killed firefighter Robert "Bobby" Kilduff Jr. in May began when several lithium-ion batteries overheated inside plastic toolboxes, Fire Commissioner Rodney Marshall said on Nov. 4, The Boston Globe reported.

Speaking at a news conference at department headquarters with Mayor Michelle Wu, Marshall blamed "thermal runaway involving multiple lithium-ion batteries stored inside of plastic toolboxes." The fire started on an enclosed rear porch on the third floor of a home on Treadway Road in Savin Hill, according to the Globe. Officials would not say what devices the batteries powered and have released few details about how Kilduff died, the Globe reported.

"He made the ultimate sacrifice in service to our city," Wu said at the news conference, according to the Globe.

The Globe reported that the alarm came in about 8:05 p.m. on May 23 and that crews called a second and third alarm. Around 8:30 p.m., radio traffic indicated the bulk of the fire was under control; about 20 minutes later, a mayday call reported Kilduff had gone off the third-floor porch. He died at a hospital of injuries from the fall. Firefighters got all five residents out and kept the flames from spreading, the paper reported.

According to the Globe, Kilduff, known at the firehouse as "BK," was a Marine Corps veteran and third-generation firefighter with 24 years in the department, assigned to Rescue Company 2, a specialized unit that answers the most dangerous calls. The Globe reported he was the first Boston firefighter to die on duty in over 10 years.

District Chief Keith Kelly said such batteries "burn without oxygen because they generate their own," and urged people to buy certified batteries, charge them with the proper cable on a hard surface and never charge one that is swollen or leaking, the Globe reported.

Statewide, Massachusetts firefighters have responded to 112 lithium-ion battery fires in 2026, Department of Fire Services spokesperson Jake Wark told the Globe in a separate report. Since 2023, the state has logged 362 such fires, at least 49 injuries and four deaths, he said, adding that the figures are probably an undercount.